In the offshore oil exploration field, the tubes and their end coupling members must resist tensile loads capable of reaching, in normal conditions of use, about a million Newtons.
The metallic tubes with metallic end coupling members used in oil exploration resist such loads.
Various industrial methods have been developed to produce composite tubes fitted with metallic end coupling members and capable of withstanding the significant tensile loads. The composite tubes have substantial advantages over metallic tubes because of their fatigue strength, corrosion resistance and lower weight.
According to a method described in French patent FR-A-2,509,011 by the applicants, a conical metallic insert is placed at the end of a composite tube. Between the outer surface of this end and the inner wall of the tube, an elastomeric layer is applied and adhesively bonded onto this outer surface, so that the loads are transmitted through the elastomeric layer. After a first polymerization of the tube, a second metallic member in the shape of a shell is applied on the polymerized composite, and is then hooped by a circumferential winding, for example of glass fibers. The metal/composite bond can also be provided through another elastomeric layer by a second curing to provide the polymerization of the outer hooping and the adhesive films.
A further method, described in EP-A-0,093,012, enables the joining of a tube made up of filament windings and of another body. Tubular and hollow metallic envelopes are interposed between fiber layers made up of filament windings, spaced in the radial direction, this being done at the ends. The connection is provided by securing devices which pass through the composite and the metallic envelopes. In this case, the tensile load applied to the metallic end coupling member is transmitted to the composite structure by a "hammering" effect.
According to yet another method described in French Patent FR-A-2,641,841 by the applicants, essentially longitudinal fibers are would continuously around a cylindrical mandrel in order to constitute the running part of the composite tube and, at the same time, around a metallic bi-conical shaped end coupling member. These longitudinal fibers are next bound to the metallic end coupling member by circumferential fibers before providing a final polymerization of the tube. Supplementary means are provided to enhance the integration of the end coupling member in the tube, and thus, limit the tube elongation.
These methods provide tubes which can be described as "rigid" by contrast with the "flexible" or "supple" metallic tubes, and which can withstand the tensile loads of the exploitation conditions of oil exploration at sea, while offering a minimal elongation under the internal pressure. However, such tubes all have the drawback that the length of the finished tube must be known before proceeding to the fabrication of the running part of the tube, that is to say the arrangement of filament windings.
In fact, in the three techniques referred to above, the winding of the filament layers constituting the tube is carried out on a mandrel bearing the connecting fittings, or end coupling members, of the tubes. These fittings are then wrapped by the fibers, and thus, "fixed" to the composite material.
Thus, it is not possible to produce and stock composite tubes until such time as the required length of the tube, equipped with connecting and coupling members, is known.